Method for Manufacturing plated film, cathode roll for plating, and method for manufacturing circuit board

ABSTRACT

A method for manufacturing a plated film by bringing a film having a conductive surface into electrical contact with a cathode roll with a liquid film interposed between the film and the cathode and forming a metal plating on the conductive surface of the film, characterized in that the relation E 0 &gt;[(I/Cs)×d]/σ where E 0  is the reduction potential of the metal forming the plating, I is the value of the current flowing through the cathode roll for plating, Cs is the area of the conductive surface of the film in electrical contact with the cathode roll with a liquid film interposed therebetween, d is the thickness of the gap between the cathode roll and the conductive film, and σ is the conductivity of the liquid forming the liquid film present in the gap. A cathode roll having a surface roughness Rmax of 1 μm or less is also disclosed. Further a cathode roll having a Vickers hardness of the surface of 200 or more is disclosed.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a platedfilm, a cathode roll for plating, and a method for producing a circuitboard.

The invention relates to an improvement in a method for manufacturing aplated film, in which a film carrying means for carrying a film having aconductive surface, a cathode roll, and a plating bath arranged in theupstream and/or downstream side of the cathode roll and accommodatedwith a plating solution and an anode are used in such a manner thatwhile the film is carried by the film carrying means, the conductivesurface of the film is brought into electrical contact with the cathoderoll through a liquid layer, and passed through the plating bath forforming a plating layer on the conductive surface of the film.Furthermore, the invention relates to an improvement of the cathoderoll. Still further, the invention relates to a method for manufacturinga circuit board, comprising the step of forming a circuit pattern on theplated film manufactured by the method for manufacturing a plated film.

The invention can be preferably used for producing a plated resin film.

The invention allows the production of a plated film having good surfaceproperties. Since the plated film produced by the invention issubstantially free from proj ected or depressed flaws on the platinglayer formed, it can be preferably used for producing a circuit board byforming a superfine circuit pattern at a wire pitch of 80 μm or less.

The invention can be preferably used for producing a plated film inwhich an electroplating layer is formed on a vapor-deposited metal layerof a film having the vapor-deposited metal layer formed by metalevaporation, that is, which has a layered-laminate comprising avapor-deposited metal layer and an electroplating layer formed on it.

The invention can be preferably used for producing a plated filmcomprising a film, an electroless plating layer formed on the film by anelectroless plating and an electro plating layer formed on theelectroless plating layer, that is, which has a layered-laminateconsisting of an electroless plating layer and an electroplating layerformed thereon. These plated films can be used as parts of electronicapparatuses and contribute to the size reduction and weight reduction ofthe parts. Furthermore, they can be respectively preferably used as atwo-layer flexible printed wiring board free from an adhesive favorablein view of cost reduction. The two-layer flexible printed wiring boardcan be used, for example, for TAB, COF and PGA in semiconductorpackaging.

BACKGROUND ART

Methods for continuously forming a plating layer on a surface of a filmwhile carrying the film are described in JP-A-07-22473 andJP-A-2001-192793. In these methods, a conductive surface of anon-metallic film or a metallic film is brought into contact with acathode roll, and the film is carried and passed through a plating batharranged in the upstream and/or downstream side of the cathode roll andaccommodated with a plating solution and an anode, for forming a platinglayer on the conductive surface in the plating bath. In these methods,plural units, each consisting of a cathode roll and a plating bath, areinstalled, and the film is carried and passed through the plural platingunits one after another, to form a plating layer having a desiredthickness on the conductive surface of the film.

Substrates for flexible circuits are used in electronic apparatuses,electronic parts, semiconductor packages, etc. As one of the substrates,a wiring board consisting of a polyimide film or polyester film and acopper foil is used. As the wiring boards, there are a board usuallycalled “a three-layer type” in which a copper foil is stuck to a filmthrough an adhesive and a board usually called “a two-layer type” inwhich a metallic layer is formed on a film by means of plating or thelike without using an adhesive. Recently the wiring of circuits isformed at a finer pitch, and among these board types, the lattertwo-layer type attracts more attention.

In a three-layer board for printed circuit, an epoxy-based resin oracrylic resin is used as the adhesive. This board has a disadvantagethat the electric properties are deteriorated due to impurity ionscontained in the adhesive. The heat resistance temperature of theadhesive of the board is from 100° C. to 150° C. and therefore, in thecase where a polyimide film is used as the base film, the board has adisadvantage that the high heat resistance of the film of 300° C. orhigher cannot be sufficiently utilized. As a result, in the wire bondingto an IC chip in need of high temperature, the heating temperature usedmust be lowered.

In a three-layer board for printed circuit, the general thickness of thecopper foil is 18 μm or 35 μm. Therefore, in the case where patterningis performed at a wire pitch of 80 μm (the copper wire width: 40 μm andthe inter-wire gap: 40 μm) or less, copper is so thick as to remarkablylower the etching rate, and in addition, the circuit width on thesurface side of the copper foil becomes very different from the circuitwidth of the adhesive side. Otherwise, there occurs a phenomenon thatetching makes the entire circuit width very thin, not allowing a desiredcircuit pattern to be obtained.

To solve the above-mentioned problems in the three-layer type, atwo-layer board for printed circuit free from the use of an adhesive isproposed. A two-layer board can be produced by vapor-depositing any ofvarious metals on a film by any of various vapor deposition methods suchas vacuum evaporation, sputtering or any of various ion plating methods(including PVD method, CVD method of vaporizing chemicals including ametal for deposition), to form a conductive surface, or plating a filmwith any of various metals by an electroless plating method to form aconductive surface, and subsequently electrolytically plating theconductive surface with copper.

In a two-layer board, the thickness of the copper layer can be changedfreely by means of electrolytic copper plating. For example, if a copperlayer having a thickness of 8 μm is obtained, a circuit pattern at awire pitch of 60 μm can be simply produced, and the heat resistance ofany of various base films can be sufficiently utilized. Based on suchsituation, the demand for plated films is growing.

However, when a continuously carried film is plated, the magnitude ofthe tension acting on the film in the carrying process cannot be solarge in view of the stiffness of the film.

Furthermore, unless there is certain slipperiness between the carriedfilm and the cathode roll, the carried state of the film is disturbed bythe cathode roll, and the carrying tension is unbalanced at pluralportions in the width direction of the film. The unbalance causes thecarried film to be wrinkled and creased, making the carried stateunstable.

With regard to this problem, in the conventional apparatus, the runningfilm that accompanies the plating solution taken from the plating bathreaches the cathode roll, to form a liquid layer on the cathode roll,and this liquid layer solves the problem. The liquid layer gives someslipperiness between the film and the cathode roll. The slipperinessprevents that the carried state of the film becomes unstable at pluralportions in the width direction of the film.

Furthermore, as described in JP-A-2001-192793, if the carried film is ametallic foil such as a copper foil, the carrying tension of the filmcan be made large, and the surface resistance value can also be keptsmall, allowing perfect conduction with the cathode roll to be achieved,without causing any problem.

However, as described in JP-A-07-22473, if it is attempted to carry apolyimide film having a thickness of 50 μm, the film may be fractured inview of the Young's modulus and strength of the film, etc. Furthermore,an internal stress may work in the formed plating layer. Therefore, alarge tension cannot be applied to the film, and employed is a method offorming a plating layer while the carried state of the film is balancedunder a relatively low film tension. That is, a liquid layer containinga plating solution is interposed between the cathode roll and the film,for causing adequate slipperiness between the cathode roll and the film,to stabilize the carrying of the film.

However, even in this method, if an electric current is fed from thecathode roll for forming a plating layer, it often occurs that the metalintended to constitute the plating layer is precipitated and depositedon the cathode roll.

There occurs a phenomenon in which the metal deposited on the cathoderoll is brought into the plating bath by the film and acts as nuclei inthe plating bath, to form abnormal projections (projection defects) onthe conductive surface or the plating layer surface due to electricfield concentration. There also occurs a phenomenon in which the metaldeposited on the cathode roll forms depressions in the film or flaws theconductive surface or plating layer surface. The thickness of theplating layer formed further subsequently is not enough to flatten thedepressions or the flawed portions. As a result, the surface of theplated film produced has depression defects. Moreover, the patterns ofthe metal deposited on the cathode roll are transferred to theconductive surface of the film, to cause a problem of degrading thesurface appearance quality.

The depression and projection defects formed on the surface of theplated film may cause such non-conformances as wire breaking in theetching step for forming circuit wiring or in the step of bonding ICchips and the like in the circuit mounting process, to cause a problemthat the quality of the circuit cannot be guaranteed.

The method for inhibiting the precipitation of the metal intended toconstitute the plating layer on the cathode rolls causing such problemsis not yet found. At present, after the apparatus has been operated fora certain time, the production is sopped, and the metal precipitated anddeposited on the cathode rolls is scraped off. Then, the operation ofthe apparatus is resumed. The metal removal from the cathode rollsremarkably lowers the productivity of the plated film.

On the other hand, the conventional cathode rolls are formed of aniron-based material. Furthermore, the plating solution is based onsulfuric acid, and it often contains hydrochloric acid. Therefore, thecathode rolls have a problem that the selection of the material forcorrosion prevention is difficult. In this situation, SUS316 has beensuitably used as a material resistant against the plating solution.However, even the SUS316 has a problem that intergranular corrosion iscaused after it has been used for a certain time.

The cathode rolls function also as rolls for carrying the film. Thecathode rolls have a problem that they are rubbed by the running filmand are gradually flawed. Therefore, if the cathode rolls are used forproduction for a certain time, they are flawed to increase thefrictional force with the film, causing such a state that the film isgripped. This state causes the film to be tensioned and deflected andfurther causes it to sway irregularly in the horizontal direction,thereby wrinkling it during the carrying process. In the worst case, therunning film is creased.

Furthermore, as the case may be, it can happen that the metal intendedto constitute the plating layer, for example, copper is precipitated anddeposited on the cathode rolls. If the deposit, for example, copper isscraped off for being removed, using a sponge containing an abrasive,the SUS316 used as the material constituting the cathode rolls is oftenflawed.

The flaw patterns are transferred to the plating layer, for example,copper layer of the plated film produced. The plated film having thetransferred flaws has surface appearance quality defects called hairlines. The hair lines are depression flaws, and cause wire breaking inthe etching step for forming circuit wiring and in the step of bondingIC chips in the circuit mounting process. As a result, the quality ofthe produced circuit may not be able to be guaranteed.

Moreover, the cathode rolls used for plating are heavily consumed due toflawing. In the case where the cathode rolls are used for continuousproduction, they must be exchanged for being reground after use for twoweeks or about one month. This greatly increases the maintenance workand cost of the apparatus, to lower productivity, hence to raise theproduction cost.

To solve this problem, JP-3135176 proposes a method in which a platingsurface, for example, copper surface in a product of a flexible circuitboard is not brought into contact with a cathode roll. This is aso-called contact-less carrying method and at now it is used formanufacturing a plated film. An outline of this method is shown withFIG. 17. In FIG. 17, carrier rolls 52 and 53 have large-diameter discs52 a, 52 b, and 53 a, 53 b at their both ends respectively. A film 50 iscarried by being guided both edge portions 51 a, 51 b of the film 50with these discs. In FIG. 17, symbol W denotes the overall width of thefilm 50, and symbol Wa denotes the width of the non-contact portion.When the film 50 is carried, a liquid is made to flow from the inside ofthe carrier roll 53 toward the outside, for letting a force for biasingthe film 50 toward outside acts on the film 50. The liquid is fed from aliquid source 55 through a flow rate control unit 56, being injectedfrom the respective nozzle holes 58 of a nozzle pipe 57.

However, if the film 50 is carried by this method, the liquid giving abiasing force from the inside of the roll becomes unstable, and the film50 deviates from the large-diameter portions (disc portions) of thecarrier roll, not allowing continuous production. Furthermore, in thecase where the carrier roll 53 is a cathode roll, when the power issupplied from both the ends, the power supply area is small, and thepower supply is likely to be unstable. As a result, the thickness of theformed plating layer becomes irregular. The cathode roll for plating isheavily consumed, and in the case of continuous production, the cathoderoll for plating must be exchanged for being reground after use of twoweeks to about one month. This greatly increases the maintenance workand cost of the apparatus, to lower the productivity and to raise theproduction cost.

Electric and electronic apparatuses are being substituted by IC version,and become more highly dense and more highly integrated at a rapid pace.In this connection, the wire pitch of patterns of flexible printedcircuit boards become finer from a pitch ranging from 150 to 200 μm to apitch ranging from 80 to 150 μm, and presently there is a demand forproducing patters at a wire pitch ranging from 30 to 80 μm. In future, ademand for producing patterns at a wire pitch of less than 80 μm isexpected to arise.

An object of the invention is to provide a method for producing a platedfilm that solves the above-mentioned problems of the prior art and canmeet the above-mentioned demand.

Another object of the invention is to provide a cathode roll usable inthe method for producing a plated film that can solve theabove-mentioned problems of the prior art and can meet theabove-mentioned demand.

DISCLOSURE OF THE INVENTION

A method for producing a plated film of the invention is that a filmcarrying means for carrying a film having a conductive surface, acathode roll, and a plating bath arranged in the upstream and/ordownstream side of the cathode roll and accommodated with a platingsolution and an anode are used in such a manner that while the film iscarried by the film carrying means, the conductive surface of the filmis brought into electrical contact with the cathode roll through aliquid layer, and passed through the plating bath for forming a platinglayer on the conductive surface of the film, characterized in that thefollowing relation is satisfied:E ₀>[(I/Cs)×d]/σwhere E₀ is the reduction potential of a metal constituting the platinglayer; I is the value of a current flowing through the cathode roll forplating; Cs is the area of the conductive surface of the film inelectrical contact with the cathode roll through the liquid layer; d isthe thickness of a gap between the cathode roll and the conductivesurface of the film; and σ is the conductivity of a liquid constitutingthe liquid layer.

It is preferred that the conductivity of the liquid constituting theliquid layer existing in the gap is controlled by means of theconcentration of an electrolyte mainly composed of sulfuric acid.

It is preferred that the conductivity of the liquid constituting theliquid layer existing in the gap is from 1 mS/cm to 100 mS/cm.

It is preferred that the thickness d of the gap is from 20 μm to 500 μm.

It is preferred that the thickness d of the gap is controlled by meansof a carrying tension of the film.

It is preferred that the carrying tension of the film is from 10 N/m to320 N/m.

It is preferred that the plating layer is composed of copper.

It is preferred that the film is made of a polyimide resin or polyesterresin.

It is preferred that a material for constituting the plating layer andprecipitated on a surface of the cathode roll is removed by means of ablade and/or an elastic body provided in contact with the surface of thecathode roll.

It is preferred that a liquid is supplied continuously or intermittentlyto at least one of the cathode roll, the blade and the elastic body.

A cathode roll for plating of the invention, used for producing a platedfilm by a method, in which a film carrying means for carrying a filmhaving a conductive surface, a cathode roll, and a plating bath arrangedin the upstream and/or downstream side of the cathode roll andaccommodated with a plating solution and an anode are used in such amanner that while the film is carried by the film carrying means, theconductive surface of the film is brought into electrical contact withthe cathode roll through a liquid layer, and passed through the platingbath for forming a plating layer on the conductive surface of the film,is characterized in that the surface roughness Rmax of the cathode rollis 1 μm or less.

A cathode roll for plating of the invention, used for producing a platedfilm by a method, in which a film carrying means for carrying a filmhaving a conductive surface, a cathode roll, and a plating bath arrangedin the upstream and/or downstream side of the cathode roll andaccommodated with a plating solution and an anode are used in such amanner that while the film is carried by the film carrying means, theconductive surface of the film is brought into electrical contact withthe cathode roll through a liquid layer, and passed through the platingbath for forming a plating layer on the conductive surface of the film,is characterized in that the Vickers hardness of the cathode roll is 200or more.

In the cathode roll for plating of the invention, it is preferred that asurface layer mainly composed of tungsten is formed thereon.

In the cathode roll for plating of the invention, it is preferred that asurface layer containing 50% or more of tungsten and further containingat least one element selected from the group consisting of chromium,nickel and carbon is formed thereon.

In the cathode roll for plating of the invention, it is preferred that asurface layer containing 60 to 80 wt % of tungsten, 15 to 25 wt % ofchromium, 1 to 10 wt % of nickel, and 1 to 10 wt % of carbon is formedthereon.

In the cathode roll for plating of the invention, it is preferred thatthe surface thereof is treated by a thermal spraying method.

It is preferred that the thermal spraying method is a denotation flamespraying method.

It is preferred that the porosity of a thermally sprayed layer formed bysurface treatment based on the thermal spraying method is 2% or less.

If the cathode roll for plating of the invention is used as the cathoderolls for carrying out the method for producing a plated film of theinvention, plural films are allowed to run in parallel to each otheralong the cathode rolls.

The method for producing a circuit board of the invention ischaracterized in that a circuit pattern is formed on a plated filmproduced by the method for producing a plated film of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical sectional view showing a mode of theapparatus for producing a plated film, used for carrying out theinvention.

FIG. 2 is a schematic vertical sectional view partially showing thecathode rolls and the plating bath in the apparatus of FIG. 1.

FIG. 3 is a schematic vertical sectional view showing a mode of acathode roll unit used for carrying out the invention.

FIG. 4 is a schematic vertical sectional view showing another mode of acathode roll unit used for carrying out the invention.

FIG. 5 is a graph showing the relationships between gaps andconductivities at respective current values applied to respectiverectifiers.

FIG. 6 is a schematic perspective view showing a measuring instrumentfor measuring the thickness of a liquid layer on a cathode roll.

FIG. 7 is a plan view showing the carried positions of the films inExamples 3 and 4.

FIG. 8 is a schematic perspective view showing a measuring instrumentfor measuring the tensions of the films in Examples 3 and 4.

FIG. 9 is a graph showing the carried positions of the films in Example3.

FIG. 10 is a graph showing the carried positions of the films in Example4.

FIG. 11 is a graph showing the carried positions of the films inComparative Example 3.

FIG. 12 is a graph showing the carried positions of the films inComparative Example 4.

FIG. 13 is a graph showing the results of measuring the tensions of thefilms in Example 3.

FIG. 14 is a graph showing the results of measuring the tensions of thefilms in Example 4.

FIG. 15 is a graph showing the results of measuring the tensions of thefilms in Comparative Example 3.

FIG. 16 is a graph showing the results of measuring the tensions of thefilms in Comparative Example 4.

FIG. 17 is a perspective view showing the conventional non-contactcarrying device for a film disclosed in JP-3135176.

THE BEST MODES FOR CARRYING OUT THE INVENTION

A mode of the method for producing a plated film of the invention isexplained below in reference to drawings.

FIG. 1 schematically shows a continuous electroplating apparatus as awhole in which a film 4 a having a conductive surface is continuouslyunwound and carried from a film unwinding means 306 by a film carryingmeans, and plated in a plating bath 6, being wound as a plated film 4 bby a film winding means 324.

The process for producing the plated film 4 b in the apparatus comprisesa film supplying step 301 for unwinding the film 4 a having a conductivesurface from a roll film, a pre-treatment step for, for example,treating the conductive surface of the film 4 a with acid treatment,degreasing treatment, water washing, etc., an electroplating step 303for forming a plating layer on the conductive surface, a post-treatmentstep 304 for removing or washing away the plating solution, treating forrust prevention, washing away the treatment residue, and further drying,and a winding step 305 for winding the produced plated film 4 b into afilm roll. In the case where the conductive surface of the film 4 a isclean, the pre-treatment step 302 can be omitted. In the case where itis not necessary to post-treat the produced plated film 4 b, thepost-treatment step 304 can be omitted.

In FIG. 1, the film 4 a having a conductive surface unwound from thefilm unwinding means 306 is adjusted in its carrying tension while itpasses through an accumulator 307 and further through a balance rollsection 308. Subsequently, the running film 4 a is controlled to besubstantially constant in the running speed, while it passes through aspeed control roll section 309. Then, the running film 4 a passesthrough an acid treatment and degreasing treatment section 310 and awater washing section 312 and is introduced into the plating bath 6containing a plating solution 7. Part of the plating bath 6 is shown inFIG. 2 as an enlarged view.

In FIG. 2, the film 4 a runs along a cathode roll 1-1 while itsconductive surface is kept in electrical contact with the cathode roll1-1, and is then introduced into the plating bath 6. In the plating bath6, the film 4 a passes along a submerged roll 101-1 and is raised out ofthe plating bath 6, reaching the next cathode roll 1-2.

The plating bath 6 accommodates cases 102-1 and 102-2 respectivelypacked with accumulated copper balls. The cases 102-1 and 102-2 act asanodes 2. The cathode rolls 1-1 and 1-2 act as cathodes. The electriccurrent from a rectifier (DC power source) 3-1 flows between the anodesand the cathodes. In the plating bath 6, shielding plates 106-1 and106-2 are provided for the respective anodes 2. This constitution formsone plating unit 6 a surrounded by a one-dot-dash-line in FIG. 2.

Similarly the subsequent unit consists of cathode rolls 1-2 and 1-3acting as cathodes, an submerged roll 101-2, cases 102-3 and 102-4respectively packed with accumulated copper balls and acting as anodes2, shielding plates 106-2 and 106-3, and a rectifier (DC power source)3-2. In the electroplating apparatus shown in FIG. 1, many such platingunits 6 a are disposed continuously from the upstream side to thedownstream side in the film 4 a carrying direction. The film 4 a passesthe respective units 6 a one after another, to be increased in thethickness of the plating layer formed on its conductive layer.

It is preferred that the electric current condition in the respectiveunits 6 a is selected to ensure that the current density for the film 4a can be kept in a range from 0.2 to 10 A/dm². The definition of thecurrent density is described later. On the conductive layer of the film4 a coming out of the last unit 6 a after passing the respective units 6a one after another, a plating layer having a thickness of 1 to 30 μm isformed.

In the bottom of the plating bath 6, air inlets (nozzles for airstirring) 330-1, 330-2, 330-3 and 330-4 are provided. It is preferredthat fresh air 331-1, 331-2, 331-3 and 331-4 is introduced from theseair inlets and released into the plating solution 7, for stirring theplating solution 7 in the plating bath 6. This improves the uniformityof the formed plating layer. In this case, supplying fresh air to theregion where the plating layer is formed is effective for improving theuniformity of the plating layer. The reason is that the concentration ofthe metal ions destined to form the plating layer near the surface ofthe formed plating layer is enhanced.

Though not shown in the drawing, it is preferred that the platingsolution 7 in the plating bath 6 is let out of the plating bath,filtered to get rid of contaminants, and introduced into the platingbath 6 in constant circulation.

The plated film 4 b coming out of the plating bath 6 after completion ofplating layer formation passes along a roll 325 used for detecting thetension of the film. Subsequently, the plated film 4 b passes through awater washing step 314 for treating the film using washing water 315 forremoving the adhering plating solution, a rust prevention treatment step316 for protecting the formed plating layer using a rust preventiontreatment liquid 317, a water washing step 318 for removing theexcessive rust prevention treatment liquid, and a drying step 320 havinga drying furnace used for removing water, one after another.

The plated film 4 b coming out of the drying step 320 passes through aspeed adjusting section 321 and a balance roll section 322, to beadjusted in its tension. The plated film 4 b adjusted in its tensionpasses through an accumulator 323 and wound as a film roll by a filmwinding means 324.

FIG. 3 is an enlarged vertical sectional view showing an example of thecathode roll unit used in the plated film production process forcarrying out the plated film production method of the invention. Thecathode roll unit comprises a cathode roll 1, an electrolyteaccommodating pan 10, an adjusting tank 11 for adjusting theelectrolyte, and an electrolyte supply device consisting of pipes 13 and16 for supplying the electrolyte to the electrolyte accommodating pan10.

In FIG. 3, the film 4 a having the conductive surface 5 is kept inelectrical contact with the cathode roll 1, with the conductive surface5 turned on the side of the cathode roll 1, while it runs in theclockwise direction in FIG. 3, being carried into the plating bath 6.The cathode roll 1 is connected with a motor (not shown in the drawing),and rotated in the clockwise direction in FIG. 3.

A liquid layer 8 is interposed between the conductive surface 5 of thefilm 4 a and part of the circumferential surface of the cathode roll 1.Symbol d denotes the thickness of the liquid layer 8.

Below the cathode roll 1, the electrolyte accommodating pan 10 isinstalled. The electrolyte accommodating pan 10 is supplied with aconcentration-controlled electrolyte 9. In the electrolyte 9, part ofthe cathode roll 1 is immersed. The cathode roll 1 is rotated while itis incessantly bathed in the electrolyte 9. With the rotation, theelectrolyte 9 is supplied to the region where the liquid layer 8 isformed. As a result, the liquid layer 8 is formed between the conductivesurface 5 of the film 4 a and the surface of the cathode roll 1.

The electrolyte 9 is supplied from the adjusting tank 11 accommodating aconcentration-controlled electrolyte 12 through the pipes 13 and 16 tothe electrolyte accommodating pan 10. The pipes 13 and 16 are providedwith a liquid feed pump 14 and a valve section (electromagnetic valve)15. The amount of the electrolyte 12 supplied to the electrolyteaccommodating pan 10 is strictly controlled by the action of the valve15 or by the action of the pump 14. The electrolyte 9 in the electrolyteaccommodating pan 10 changes in concentration, since the platingsolution of the plating unit 6 a (FIG. 2) positioned on the upstreamside in the running direction of the film 4 a is brought into theelectrolyte accommodating pan 10. To prevent the concentration change,the electrolyte is discharged from a discharge port 17, and theconcentration-adjusted electrolyte 12 is supplied from the pipe 16.

The rectifier 3 supplies current IA from the cathode roll 1 to the anode2 formed as a case packed with accumulated copper balls. It is preferredthat the current density in this case is selected in a range from 0.2 to10 A/dm². The current density refers to a value obtained by dividing thecurrent applied from the rectifier 3, by the area of the film 4 a in theportion immersed in the plating solution 7 of the plating bath 6.

FIG. 4 is an enlarged vertical sectional view showing another example ofthe cathode roll unit used in the plated film production process forcarrying out the plated film production method of the invention. Thecathode roll unit comprises a cathode roll 1, a liquid receiving pan 31,a doctor blade 21, an elastic body 22, and liquid supply sections 24, 27and 29.

The function of the cathode roll 1 in the cathode roll unit of FIG. 4 isthe same as the function of the cathode roll 1 in the cathode roll unitof FIG. 3. However, the cathode rolls 1 are different each other in theequipment arranged at their bottoms.

In the cathode roll unit of FIG. 4, the doctor blade 21 is provided forremoving the deposit adhering to the cathode roll 1, from the cathoderoll 1. The doctor blade 21 is supported on a support 26 in such amanner that its tip end may be kept in contact with the surface of thecathode roll 1. The liquid supply section 24 is provided for supplying aliquid 25 to the doctor blade 21.

Furthermore, the elastic body 22 is provided for removing the depositadhering to the cathode roll 1. The elastic body 22 is supported on asupport 23 in such a manner that its upper surface may be kept incontact with the surface of the cathode roll 1. The liquid supplysection 27 is provided for supplying a liquid 28 to the elastic body 22.

Moreover, the liquid supply section 29 is provided for supplying aliquid 30 to the cathode roll 1.

Though not shown in the drawing, the supplied amounts of liquids 25, 28and 30 are strictly controlled individually by means of pumps andvalves.

Lest the liquids 25, 28 and 30 should enter the plating bath 6, thereceiving pan 31 is provided, and has a discharge port 33 fordischarging the received liquid 32.

In FIG. 3, it is necessary that the following relation is satisfied, forpreventing that a metal intended to constitute the plating layer isprecipitated and deposited on the cathode roll 1.E ₀>[(I/Cs)×d]/σ  (i)where d is the thickness of the gap existing the liquid layer 8 betweenthe cathode roll 1 and the conductive surface 5 of the film 4 a; σ isthe conductivity of the liquid constituting the liquid layer 8 existingin the gap; I is the value of the current flowing through the cathoderoll 1 for plating; Cs is the area of the conductive surface 5 of thefilm 4 a kept in electrical contact with the cathode roll 1 through theliquid layer 8; and E₀ is the reduction potential of the metalconstituting the plating layer.

Actually the following is desirable. In reference to the electriccurrent condition and the reduction potential E₀ of the metal, for thecurrent value I concerned, the relation between the thickness d of thegap chosen as the abscissa and the conductivity σ chosen as the ordinateis graphed as calculated from the formula (i), and any conductivity a inthe range above the line drawn in the graph is used.

The inventors found that even in the case where the film 4 a is carriedwith its conductive surface 5 kept in electrical contact with thecathode roll 1 through the liquid layer 8, if the potential differencebetween the conductive surface 5 and the cathode roll 1 exceeds thevalue of the reduction potential E₀ of the metal constituting theplating layer, there occurs a phenomenon in which the metal intended toconstitute the plating layer is precipitated on the cathode roll 1. Theinventors variously examined how to prevent the precipitationphenomenon. As a result, the relation shown by the formula (i) wasfound.

The method for producing a plated film of the invention is characterizedin that at least one of the thickness d of the gap between the cathoderoll 1 and the conductive surface 5 of the film 4 a, the conductivity σof the liquid constituting the liquid layer 8 existing in the gap, thevalue of the current I flowing through the cathode roll 1 for plating,and the area Cs of the conductive surface 5 of the film 4 a kept inelectrical contact with the cathode roll 1 through the liquid layer 8 iscontrolled to ensure that the value of [(I/Cs)×d]/σ can be kept lessthan the value of the reduction potential E₀ of the metal constitutingthe plating layer.

In this case, the phenomenon in which the metal intended to constitutethe plating layer is precipitated on the cathode roll 1 can beprevented. In addition, since the liquid layer 8 is interposed betweenthe conductive surface 5 and the cathode roll 1, the carried state ofthe film 4 a can also be kept good.

As the liquid constituting the liquid layer 8, the electrolyte containedin the plating solution 7 can be used. It is preferred that theelectrolyte 9 used as the liquid constituting the liquid layer 8 is anelectrolyte mainly composed of sulfuric acid, since a metal salt isunlikely to be generated. In the case where the metal constituting theplating layer is copper, it is especially preferred to use anelectrolyte mainly composed of sulfuric acid.

For adjusting the conductivity of the electrolyte 9 constituting theliquid layer 8, it is desirable to monitor the conductivity of thesupplied electrolyte in the adjusting tank 11, and to use a solutionobtained by diluting highly concentrated sulfuric acid using ionexchange water or the like, for adjusting the conductivity. Theconductivity of the electrolyte adjusted in conductivity is monitored bymeans of a high precision conductivity meter. When the conductivity islower than the desired value, highly concentrated sulfuric acid issupplied into the adjusting tank 11, and when the conductivity is higherthan the desired value, ion exchange water is supplied. It is preferredthat the adjustment of conductivity is feedback-controlled.

As shown in FIG. 3, the electrolyte 9 adjusted in conductivity suppliedfrom the adjusting tank 11 is collected in the electrolyte accommodatingpan 10 positioned below the cathode roll 1. The cathode roll 1 isdisposed in relation with the electrolyte accommodating pan 10 to ensurethat part of the cathode roll 1 can be kept in contact with or immersedin the electrolyte 9 collected in the electrolyte accommodating pan 10.If the cathode roll 1 is rotated, the electrolyte 9 adhering to thesurface of the cathode roll 1 is carried to the region where the liquidlayer 8 is formed, and at the region, the liquid layer 8 is formedbetween the running film 4 a and the conductive surface 5 of the cathoderoll 1.

In the cathode roll 1 shown in FIG. 4, the liquid 25 is supplied fromthe liquid supply section 24 to the doctor blade 21. The liquid 25supplied to the doctor blade 21 is deposited on the surface of thecathode roll 1, and while the cathode roll 1 is rotated, the liquid 25is carried to the region where the liquid layer 8 is formed, to form theliquid layer 8 there between the conductive surface 5 of the runningfilm 4 a and the cathode roll 1.

Furthermore, in the cathode roll 1 shown in FIG. 4, the liquid 28 issupplied from the liquid supply section 27 to the elastic body 22. Theliquid 28 supplied to the elastic body 22 is deposited on the surface ofthe cathode roll 1, and while the cathode roll 1 is rotated, the liquid28 is carried to the region where the liquid layer 8 is formed, to formthe liquid layer 8 there between the conductive surface 5 of the runningfilm 4 a and the cathode roll 1.

Still furthermore, in the cathode roll 1 shown in FIG. 4, the liquid 30is directly supplied from the liquid supply section 29 to the cathoderoll 1. The liquid supplied to the cathode roll 1 is deposited on thesurface of the cathode roll 1, and while the cathode roll 1 is rotated,the liquid is carried to the region where the liquid layer 8 is formed,to form the liquid layer 8 there between the conductive surface 5 of therunning film 4 a and the cathode roll 1.

In the cathode roll 1 shown in FIG. 4, at least one of theabove-mentioned three methods is used as the method for forming theliquid layer 8. In any of the methods, it is only required that theconductivity of the liquid constituting the liquid layer 8 existing inthe gap d basically satisfies the above-mentioned formula (i).

In the actual production control, it is preferred that the conductivityis controlled in a range from 1 mS/cm to 100 mS/cm.

In the case where the conductivity is less than 1 mS/cm, if it isattempted to avoid that the metal intended to constitute the platinglayer is precipitated on the cathode roll 1, a low current value must beselected for the applied current. In the production process employingthe low current value, the productivity of the plated film 4 b declines.Therefore, it is not preferred that the conductivity is less than 1mS/cm, since productivity cannot be enhanced.

Especially in the case where the metal constituting the plating layer iscopper, if the plating apparatus having a size as shown in Example 1described later is used, a current value of 200 A is the limit at whichcopper is precipitated on the cathode roll 1 even if the gap d is keptas small as 40 μm. If an area of about 3.2 m×0.52 m is plated using onerectifier, the current density for forming the plating layer in thiscase can be raised only up to 1.2 A/dm² at the highest.

In the case where the conductivity is more than 100 mS/cm, the metal islikely to be dissolved out of the formed plating layer. Therefore, it isnot preferred that the conductivity is more than 100 mS/cm, since themetal dissolving phenomenon is likely to occur.

The extent of the gap d can be controlled by adjusting the carryingtension of the film 4 a. Theoretically, there is the following generallyknown Hoyle's equation (ii).d=α×r×(βμv/T)^(2/3)  (ii)where α and β are constants; r is the diameter of the cathode roll 1; μis the viscosity of the liquid of the liquid layer 8; v is the carryingspeed of the film 4 a; and T is the carrying tension of the film 4 a.

The relation between the gap d and the carrying tension T of the film 4a can be found based on this theoretical equation. However, since thereis a relation that the gap d is virtually inversely proportional to the⅔rd power of the carrying tension T, this relation can be used tocontrol the gap d and the carrying tension T.

Based on the latter method, in the case where the gap d is desired to beadjusted to its ½, it is only required to multiply the carrying tensionby 2^((3/2))≈2.83. If the gap d is controlled as described above, theproduction conditions to satisfy the formula (i) can be set.

In the production process, it is preferred that the carrying tension Tof the film 4 a is kept in a range from 10 N/m to 320 N/m. In the casewhere the carrying tension T is less than 10 N/m, it can happen that thefilm 4 a sways irregularly in the horizontal direction in the runningcourse of the film 4 a. The occurrence of this phenomenon means that thecarried state of the film is not successfully controlled in theproduction process. In the case where the carrying tension T is morethan 320 N/m, if the metal of the plating layer formed on the conductivesurface 5 of the film 4 a is internally strained, there arises aphenomenon that the formed plated film 4 b is curled. The occurrence ofthis phenomenon means that a plated film 4 a with good quality cannot beproduced.

It is preferred that the extent of the gap d is from 2 μm to 500 μm. Ifthe extent of the gap d is less than 2 μm, chances that the conductivesurface 5 of the film 4 a directly contacts the cathode roll 1 increase,partly owing to the relation with the surface roughness of the cathoderoll 1. If the frequency of direct contact increases, a plated film 4 bhaving good quality cannot be obtained. If the extent of the gap d ismore than 500 μm, it can happen that the film 4 a sways irregularly inthe horizontal direction in the running course of the film 4 a. Theoccurrence of this phenomenon means that the carried state of the filmis not successfully controlled in the production process.

The carrying tension T is detected by means of the tension detectionroll 325 (FIG. 1). The signal concerning the detected value of thecarrying tension T is used to control the film carrying speed of thespeed adjusting section 321, for ensuring that the detected value of thecarrying tension T can be kept substantially constant, and as a result,control is made to ensure that the value of the carrying tension Tbecomes substantially constant. It is desirable that the control isfeedback control.

The control of the carrying speed of the film 4 a in FIG. 1 is such thatthe cathode rolls 1 are drive rolls, and that the basic speed is set inthe speed control section 309. In this control method, the draw ratioacting on the film 4 a between the cathode rolls 1-1 and 1-2 can be set.Furthermore, in this control method, the draw ratio between respectivelyadjacent cathode rolls 1 is set to be gradually higher, and the speedadjusting section 321 controls the final carrying speed of the film 4 b.If this control method is employed, the maximum carrying tension Tmax ofthe film 4 a at the cathode rolls 1 positioned above the plating bath 6occurs at the tension detection roll 325. Therefore, the carryingtension T of the film 4 a can be controlled based on the value of themaximum carrying tension Tmax, and it is preferred to do so.

The extent of the gap d is larger when the carrying tension T issmaller. The gap d on the first cathode roll 1-1 at which the carryingtension T is lowest can also be measured to raise or lower the carryingtension T to ensure that the extent of the gap conforms to a targetvalue.

It can sometimes happen that the metal intended to constitute theplating layer is precipitated on the cathode rolls 1. For preventing it,each of the cathode rolls 1 can be provided with a blade 21 for scrapingoff the precipitated metal. It is preferred that the tip of the blade 21is inclined in the rotating direction of the cathode roll 1, instead ofbeing directed to be perpendicular to the surface of the cathode roll 1.In this constitution, even if the metal intended to constitute theplating layer should be precipitated on the cathode roll 1, theprecipitated metal can be scraped off and removed by the blade 21.

The blade 21 is supported on the support 26. The support 26 has afunction of being able to adjust the force of pressing the tip of theblade 21, in the direction perpendicular to the rotating direction ofthe cathode roll 1 (in the width direction of the cathode roll 1). Inthis constitution, adjustment can be made to ensure that the force ofpressing the tip of the blade 21 to the surface of the cathode roll 1can be kept uniform in the width direction of the cathode roll 1.

The blade 21 is provided to contact the cathode roll 1. So, it ispreferred that the material of the blade 21 is unlikely to cause a metalreaction and is unlikely to cause a cell phenomenon (oxidation-reductionphenomenon) caused due to the existence of the electrolyte at thecontact portion. From this point of view, it is preferred that the blade21 is made of a resin or ceramic. A blade made of a plastic resin canbe, for example, plastic blade “E500” produced by EL Japan Co., Ltd.,UHMW polyethylene-based blade produced by Eco Blade K.K., or fluorineresin-based TS doctor blade produced by K.K. Tokyo Seisakusho. A blademade of a ceramic can be, for example, SIC new ceramic blade produced byK.K. Tokyo Seisakusho.

The elastic body 22 used for wiping away the metal precipitated on thecathode roll 1 can also be provided in sliding contact with the surfaceof the cathode roll 1. The elastic body 22 is supported on the support23. The support 23 has a function of being able to adjust the force ofpressing the elastic body 22, in the direction perpendicular to therotating direction of the cathode roll 1 (in the width direction of thecathode roll 1). In this constitution, adjustment can be made to ensurethat the force of pressing the elastic body 22 to the surface of thecathode roll 1 can be kept uniform in the width direction of the cathoderoll 1.

The elastic body 22 is composed of a sponge, nonwoven fabric, foam orthe like. It is preferred that the material of the elastic body 22 ispolyurethane, PVA (polyvinyl alcohol), PVC (polyvinyl chloride),polyethylene, or butyl-based or neoprene-based rubbery material. Amongthem, PVA (polyvinyl alcohol) and PVC (polyvinyl chloride) areespecially preferred, since they are resistant against an electrolytemainly composed of sulfuric acid and a plating solution.

If the blade 21 and the elastic body 22 are used together, the metalprecipitated on the cathode roll 1 can be efficiently removed. Forexample, the precipitated metal that happened to remain at a portion onthe cathode roll 1 due to poor contact of the blade 21 can be wiped awayby the elastic body 22.

It is desirable to continuously or intermittently supply the liquid tothe cathode roll 1 having a metal precipitated, the blade 21 and theelastic body 22. The liquid washes away the precipitated metal. In thisconstitution, the precipitated metal can be removed more efficiently. Onthe other hand, the liquid is used as a method for keeping constant, theconductivity a of the liquid constituting the liquid layer 8 in theformula (i).

The liquid is supplied, as shown in FIG. 4, from the liquid supplysection 24, the liquid supply section 27 or the liquid supply section29. That is, the liquid 25 is supplied from the liquid supply section 24to the blade 21, and the liquid 28 is supplied from the liquid supplysection 27 to the elastic body 22. Otherwise, the liquid 30 is suppliedfrom the liquid supply section 29 to the cathode roll 1.

As the base film used for producing the plated film, a film formed of apolyimide resin or polyester resin can be preferably used. In he casewhere a copper-plated film as used for electronic circuit materials isformed, a general purpose polyester resin film can be preferably used asthe base film. In the case where solder heat resistance is required formounting circuit ICs or the like, a polyimide resin film can bepreferably used as the base film.

Particular examples of the base film include polyesters such aspolyethylene terephthalate, polyethylene-2,6-naphthalate, andpolyethylene-α,β-bis(2-chlorophenoxyethane-4,4′-dicarboxylate),polyetheretherketone, aromatic polyamides, polyallylates, polyimides,polyamideimides, polyetherimides, polyoxadiazole, halogen groupsubstitution products and methyl group substitution products of theforegoing, copolymers of the foregoing, and mixtures consisting of theforegoing and other organic polymers. The base film can also containadditives such as a lubricant and a plasticizer.

As the base film, especially preferred is a film improved is inmechanical properties obtained by biaxially stretching a cast filmobtained by melt-extruding a polymer containing 85 mol % or more ofrecurring units represented by the following formulae.

(where X denotes a H, CH₃, F or Cl group)

As the base film, also preferred is a film obtained by wet-forming ordry-forming a polymer containing 50 mol % or more of recurring unitsrepresented by the following formulae, or a film obtained by biaxiallystretching and/or heat-treating the film.

(where X denotes a H, CH₃, F or Cl group; and m and n denote,respectively independently, an integer of 0 to 3)

For flexible circuits, base films having a thickness of 6 to 125 μm areoften used, and especially base films having a thickness of 12 to 50 μmare suitably used.

It is very difficult to let a wide film having such a thin thicknesssmoothly run in the plated film production apparatus shown in FIG. 1. Itcan happen that even if the liquid layer 8 exists between the conductivesurface 5 of the film 4 a and the cathode roll 1, the film 4 a does notrun smoothly.

In the case where the surface roughness Rmax of the cathode roll 1 ismore than 1 μm, when the carrying tension T is raised, it can happenthat the heights of the surface projections existing on the surface ofthe cathode roll 1 become higher than the thickness d of the interposedliquid layer 8, to cause a phenomenon that the surface projections bitethe film 4 a. If this phenomenon occurs, the film 4 a is gripped by thesurface of the cathode roll 1. As a result, the film 4 a is locallytensioned, and in response to it, it is also locally loosened.

If this state occurs, the conductive surface 5 of the film 4 a or thesurface of the plating layer just formed is flawed. Furthermore, therealso occurs a problem that the surface roughness of the cathode roll 1is transferred to the conductive surface 5 of the film 4 a.

The cathode roll for plating of the invention solves the problem, bykeeping the surface roughness Rmax of the cathode roll at 1 μm or less.If this cathode roll is used, the liquid layer lubrication on thecathode roll is smooth even if the film is thin, and the film can bestably carried through the production apparatus.

However, if the cathode roll is made of ordinary SUS316, intergranularcorrosion progresses little by little with the lapse of service time.Furthermore, since the surface hardness is about 70 in Vickers hardnessHv, the surface is gradually worn and flawed due to the friction withthe film. As a result, the surface roughness Rmax of 1 μm or less cannotbe maintained, and the surface appearance quality of the productdeclines.

To solve this problem, various methods were examined. As a result, amethod of using a material having a hardness higher than that of themetal constituting the plating layer, for forming the surface of thecathode roll was found effective. In this constitution, the increase ofthe surface roughness Rmax by the wear of the cathode roll can beprevented. The Vickers hardness of copper constituting the plating layeris about 170.

The inventors variously examined a cathode roll having a high Vickershardness, especially examined the surface treatment. As a result, asurface-treated layer mainly using tungsten was found to be very good.Furthermore, it was found that a surface-treated layer containing 50% ormore of tungsten and further containing at least one or more elementsselected from chromium, nickel and carbon is preferred. Stillfurthermore, it was found that a surface-treated layer containing 60 to80 wt % of tungsten, 15 to 25 wt % of chromium, 1 to 10 wt % of nickeland 1 to 10 wt % of carbon is more preferred. Such a material isresistant against the plating solution mainly composed of sulfuric acidand further containing hydrochloric acid and the like, and is verypreferred.

As the surface treatment methods there are PVD methods such as vacuumevaporation method and sputtering method, CVD method, thermal sprayingmethod, ion injection method, plating method, etc. Among them, thesurface treatment by a thermal spraying method is preferred, since avery hard layer can be simply produced. Furthermore, a thermal sprayingmethod is preferred, since a thicker layer can be easily formed forallowing the surface roughness to be easily adjusted by a diamondgrinder after completion of surface treatment.

Thermal spraying methods include an oxy-fuel spraying method, electricspraying method, flame spraying method such as powder flame sprayingmethod, wire flame spraying method, rod flame spraying method, ordetonation flame spraying method, electric arc spraying method, andplasma spraying method. A detonation flame spraying method that allows acompact tungsten carbide-based layer to be formed is very preferred.

Lest the plating solution should erode the base metal, it is preferredthat the thickness of the surface-treated layer is 30 μm or more.Furthermore, in view of durability, it is preferred that the thicknessof the surface-treated layer is 100 μm or more. Moreover, lest theplating solution should erode inside the sprayed layer, it is preferredthat the porosity of the thermally sprayed layer is 2% or less.

If the cathode roll for plating as described above is used, it can beprevented that the film surface is flawed. Furthermore, it can beprevented that an unnatural grip force generated by the cathode rollacts on the film, and the film can be carried stably. As a result ofthese benefits, a good plating layer can be formed on the film.

Such cathode rolls allow plural films to run in parallel to each otheralong them. In the case where the cathode rolls are used, even if pluralfilms are made to run side by side simultaneously, it does not happenthat random tensions occur with the plural films, and the respectivefilms can be carried well. In a process having a long running course inwhich the films turn back very often along many cathode rolls andsubmerged rolls, the cathode rolls of the invention exhibit a very goodeffect. In this constitution, a large quantity of plated films can beproduced in a limited space, and the production efficiency of platedfilms to have been low can be dramatically enhanced.

EXAMPLES

Examples of the invention are described below. The invention is notlimited thereto or thereby. In the following examples, respectiveproperties were measured according to the following methods.

(1) Surface Tension of Plastic Film

The surface tension of a plastic film was measured according to JIS K6766-1977 (Wet Test Methods for Polyethylene and Polypropylene). Whenthe surface tension was 56 dynes/cm or less, a mixed solution consistingof formamide and ethylene glycol monoethyl ether was used as thestandard solution, for measuring the surface tension, and when thesurface tension was in a range from 57 to 73 dynes/cm, a mixed solutionconsisting of water (72.8 dynes/cm) and ethylene glycol (47.7 dynes/cm)was used.

(2) Contact Angle

An ACE contact angle meter produced by Kyowa Interface Science Co., Ltd.was used to measure the contact angle by a liquid droplet method.

(3) Thickness of Sputtered Layer

A surface roughness tester of tracer method was used for measurement. Asample was partially coated with an ink removable by a solvent, before asputtered layer was formed, and then the sputtered layer was formed, theink coating being removed for measurement.

(4) Thickness of Plating Layer

A plating layer was partially removed using an etchant, and the leveldifference was measured using a laser microscope produced by KeyenceCorporation.

(5) Conductivity

Conductivity meter CEH-12 produced by Horiba Advanced Techno Co., Ltd.was used for measurement. The measuring method was AC two-electrodemethod, and a sensor with a measuring range from 0 to 199 mS/cm wasused.

(6) Gap Existing Liquid Layer

An instrument shown in FIG. 6 was used to measure the clearancecorresponding to the thickness of the liquid layer. In the measuringinstrument shown in FIG. 6, a displacement meter 44 having a cable 43was moved along a slide guide 42 attached to a liquid layer thicknessmeasuring frame 41, and the detected signal was amplified by anamplifier unit 45, for being delivered as an amplified signal. As themeasuring sensor (displacement meter 44), a laser displacement meterproduced by Keyence Corporation was used for measuring the thickness ofthe liquid layer. As the sensor head, miniature high precision CCD laserdisplacement sensor “LK-010” was used, and as the amplifier unit 45,“LK-3100” was used. The sensor had a resolution of 0.1 μm, a spotdiameter of 20 μm and a reference distance of 10 mm.

(7) Carrying Tension

On both sides of a cathode roll, load cell type sensors were attachedfor measurement. The sensors were Model “C2G1-25K” produced by MinebeaCo., Ltd. The range in which measurement could be made was from 0 to 250N. The tension value obtained based on the weight of the roll and thecarried film contact angle was corrected.

The carrying tension during production was measured using the measuringinstrument shown in FIG. 8 as a simple method. A film 4 a was spreadalong a cathode roll 61 a, a carrier roll 62 and a cathode roll 61 b,for being carried. A push-pull gauge 63 was installed on a slide unit 65attached to a slide guide 64, and a film-pressing roll 68 was pressedagainst the film 4 a. A stopper 66 was disposed such that when thefilm-pressing roll 68 was pressed in by 15 mm, the slide stopped. Withthe roll 68 pressed in by 15 mm while the film 4 a was running, theforce received from the carried film 4 a was measured using thepush-pull gauge 63. The push-pull gauge 63 used was “Model 9550”produced by Aikoh Engineering Co., Ltd.

(8) Surface Roughness

A three-dimensional surface roughness tester of tracer method was usedfor measurement.

Example 1

In this example, a copper-plated film was applied to flexible circuitboards.

(1) Production of a Film Having a Conductive Surface

While a film was unwound from a film roll, it was treated in a pressurereducing device, and subsequently wound into a film roll. In thisapparatus, plasma treatment, the formation of a nickel chromium layer,and the formation of a copper layer were performed.

A roll of 25 μm thick, 520 mmwide and 12,500 mlongpolyimide film“Kapton” 1 (registered trademark of Du Pont, USA) was pre-arranged.

One surface of the film was treated with glow discharge plasma of argongas at a speed of 2 m/min. For the treatment, the film was carried witha distance of 2 cm kept against a rod electrode to which a high voltagewas applied, and a plasma apparatus of internal electrode system havingan electrode pair as earthed electrodes was used. The film was treatedat an argon gas pressure of 2.5 Pa, a primary output voltage of 2 kV, ahigh-frequency power supply frequency of 110 kHz and at a speed of 2m/min, to form a glow discharge plasma layer. The surface tension of thetreated film was more than 70 dynes/cm, and the contact angle was 43degrees.

Then, at an argon gas pressure of 2.6×10⁻⁶ Pa, a 30 nm nickel chromiumlayer was formed using a target consisting of 20 wt % of chromium and 80wt % of nickel by applying a DC magnetron sputtering method. Then, a 100nm copper layer was formed using a target consisting of copper havingpurity of 99.99 wt % by a DC magnetron sputtering method.

From the film, the testing portion for forming the sputtering layers andthe lead portion were removed to produce a 12,000 m film havingsputtered layers.

(2) Formation of a Plating Layer

The obtained 12,000 m film roll having sputtered layers was divided intofour 3,000 m rolls, to prepare four 520 mm×3,000 m film rollsrespectively having a conductive surface. One of them was passed throughthe following plating apparatus, to form a plating layer.

As the plating apparatus, the apparatus shown in FIGS. 1 and 3 was used.Copper was used as the anodes 2. Sixteen units, each of which was theunit 6 a surrounded by the one-dot-dash line of FIG. 2, were used toconstitute a plating circuit and a plating apparatus. A film 4 b havingan 8 μm thick copper plating layer was produced.

Each of the cathode rolls 1 was a SUS316 cylinder having a diameter of210 mm, a length of 800 mm and a wall thickness of 10 mm. When the film4 a was passed from the cathode roll 1-1 along the submerged roll 101-1to the cathode roll 1-2, the film pass length was 4 m. The pass lengthrefers to the length of the film 4 a from the vertex of the cathode roll1 to the vertex of the next cathode roll. Therefore, the total passlength of the plating section was 64 m.

The pretreatment conditions, plating conditions and rust preventivetreatment conditions of the film are shown in Table 1. The currentdensity for copper plating was set to ensure that the current densitygradually rose with increase in the number of passes along the cathoderoll 1 and the submerged roll 101. The currents set for the respectiverectifiers 3 of the first to sixteenth units were as shown in Table 2.

The relation between the gap d existing the liquid layer and theconductivity a calculated from the formula (i) for each current value inreference to the current values of Table 2 and the reduction potentialof copper of 0.337 V is expressed as a graph in FIG. 5. It is onlyrequired that the conductivity is controlled such that it is locatedabove the line indicating the current value concerned in the graph ofFIG. 5. The reduction potential of copper changes depending on theactivity or concentration of Cu ions, but the value of Cu²⁺/Cu as thestandard unit electrode potential of copper is 0.337 V. Judging from theconcentration of copper ions, the potential is smaller than this value.So, this value is employed as the reduction potential. Furthermore, thecontact area between the conductive surface 5 of the film 4 a and thecathode roll 1 was calculated to be 520 mm wide×about 220 mm, since thecontact angle was set at 120 degrees.

The clearance d corresponding to the thickness of the liquid layer wasmeasured using the laser displacement meter 44 as shown in FIG. 6, andthe film carrying tension T was set to ensure that the clearance dbecame 300 μm or less. For setting the film tension, the tension wasadequately reduced using the S-shaped lap speed control section 309shown in FIG. 1, and then, the rotating speed of each roll was changedone after another, for drawing the film at different ratios between therespectively adjacent rolls, thereby setting the respective tensions. Atthe cathode roll (tension detection roll) 325, the pressure wasautomatically detected using a load cell, and the speed of the drivemotor of the speed adjusting section 321 was used for feedback controlto ensure that the tension at the cathode roll 325 became 160 N/m. Theclearance d corresponding to the thickness of the liquid layer at thecathode roll 1-1 at which the tension was lowest was measured by thedetecting instrument of FIG. 6, and found to be 125 μm.

The carrying speed was set at 1 m/min, and the draw ratio was setstepwise when the drive forces of the motors of the respective cathoderolls 1-1 through 1-17 were set, to gradually raise the speed and togradually raise the tension.

Control can be made in such a manner that the conductivity may bedifferent at each of the units 6 a, but in this case, the apparatusbecomes expensive. So, adjustment was made to keep the conductivity ofthe liquid layer at 10 mS/cm in all of the units 6 a, to ensure that thecopper precipitation limit should not be exceeded. The sulfuric acidconcentration of the adjusting tank 11 in FIG. 3 was adjusted, and thepump 14 was set to achieve 100 ml/min, for controlling the liquidconcentration in the receiving pan 10.

As a result, copper was not precipitated on the surfaces of the cathoderolls 1, and the carried state was very stable. A roll film 4 b having agood winding style was obtained.

Later, the surface of plating copper was observed. The plating surfacehad few abnormal projections and depressions, and it was confirmed thata copper-plated film having excellent surface appearance quality couldbe produced. The numbers of abnormal projections and depressions areshown in Table 3.

(3) Formation of Patterned Circuits

The film was coated with a photosensitive liquid resist and exposed toultraviolet light using a mask of a circuit pattern having 1,024 copperwires having a wire width of 30 μm at 30 μm wire intervals, i.e., at awire pitch of 60 μm, then being developed. Ferric chloride was used asan etchant for forming patterned circuits. Fifty such patterned circuitswere observed using a stereomicroscope with a magnification of 150×, andthe quality of the patterned circuits was judged in reference tochipping (a chip of 10 μm or more was identified as a defect, and apatterned circuit having even one of 1,024 wires defectively chipped wasrejected) and wire breaking. The result is shown in Table 4. Thepatterned circuits showed a yield of 100%. TABLE 1 Process Condition 1.Degreasing Eisui Clean A110 30 g/l Temperature 50° C. Time 2 min. 2.Acid activity Sulfuric acid 10 ml/l Temperature 30° C. Time 0.5 min. 3.Cathode treatment Copper sulfate 30 g/l Sulfuric acid 150 g/lBrightening agent 3 ml/l (Ebara-Udylite) Temperature 25° C. Time 2 min.Current density 0.5 A/dm² 4. Copper plating Copper sulfate 200 g/lSulfuric acid 50 g/l Metal copper 50 g/l Brightening agent 2 ml/l(Ebara-Udylite) Chlorine 60 mg/l Temperature 30° C. Time (thickness:10μ) 20 min. Current density 0.5 → 3 A/dm²

TABLE 2 Set current Rectifier No. value 3-1   10 A 3-2   16 A 3-3   25 A3-4   32 A 3-5   45 A 3-6   68 A 3-7   95 A 3-8  135 A 3-9  155 A 3-10175 A 3-11 185 A 3-12 198 A 3-13 208 A 3-14 215 A 3-15 218 A 3-16 220 ATotal 2,000 A  

TABLE 3 Number of projections and depressions in 520 mm × 100 mm Maximumdiameter of Compara- Compara- projections and tive tive depressionsExample 1 Example 2 Example 1 Example 2 3 to 10 μm 2 5 >100 — 11 to 50μm 3 4 56 — 51 to 100 μm 0 0 32 — 101 μm or more 0 0 8 —

TABLE 4 Comparative Comparative Example 1 Example 2 Example 1 Example 2Number of 50 50 3 — acceptable circuits Circuits/50  100%  100%   6% —circuits

Example 2

In this example, a copper-plated film was applied to flexible circuitboards.

(1) Production of a Film Having a Conductive Surface

Quite the same film having a conductive surface as that of Example 1 wasproduced.

(2) Formation of a Plating Layer

The obtained 12,000 m film roll having sputtered layers was divided intofour 3,000 m rolls, to prepare four 520 mm×3,000 rolls. One of them waspassed through the following plating apparatus, to form a plating layer.

As the plating apparatus, the apparatus shown in FIGS. 1 and 4 was used.Copper was used as the anodes 2. Sixteen units, each of which was theunit 6 a surrounded by the one-dot-dash line of FIG. 2, were used toconstitute a plating circuit and a plating apparatus. A film 4 b havingan 8 μm thick copper plating layer was produced.

Each of the cathode rolls 1 was a SUS316 cylinder having a diameter of210 mm, a length of 800 mm and a wall thickness of 10 mm. When the film4 a was passed from the cathode roll 1-1 along the submerged roll 101-1to the cathode roll 1-2, the film pass length was 4 m. The pass lengthrefers to the length of the film 4 a from the vertex of the cathode roll1 to the vertex of the next cathode roll. Therefore, the total passlength of the plating section was 64 m.

The pretreatment conditions, plating conditions and rust preventivetreatment conditions of the film are shown in Table 1. The currentdensity for copper plating was set to ensure that the current densitygradually rose with increase in the number of passes along the cathoderoll 1 and the submerged roll 101. The currents set for the respectiverectifiers 3 of the first to sixteenth units were as shown in Table 2.

The relation between the clearance d corresponding to the thickness ofthe liquid layer and the conductivity σ calculated from the formula (i)for each current value in reference to the current values of Table 2 andthe reduction potential of copper of 0.337 V is expressed as a graph inFIG. 5. It is only required that the conductivity is controlled suchthat it is located above the line indicating the current value concernedin the graph of FIG. 5. The reduction potential of copper changesdepending on the activity or concentration of Cu ions, but the value ofCu²⁺/Cu as the standard unit electrode potential of copper is 0.337 V.Judging from the concentration of copper ions, the potential is smallerthan this value. So, this value is employed as the reduction potential.Furthermore, the contact area between the conductive surface 5 of thefilm 4 a and the cathode roll 1 was calculated to be 520 mm wide×about220 mm, since the contact angle was set at 120 degrees.

The clearance d corresponding to the thickness of the liquid layer wasmeasured using the laser displacement meter 44 as shown in FIG. 6, andthe film carrying tension T was set to ensure that the clearance dbecame 300 μm or less. For setting the film tension, the tension wasadequately reduced using the S-shaped lap speed control section 309shown in FIG. 1, and then, the rotating speed of each roll was changedone after another, for drawing the film at different ratios between therespectively adjacent rolls, thereby setting the respective tensions. Atthe cathode roll (tension detection roll) 325, the pressure wasautomatically detected using a load cell, and the speed of the drivemotor of the speed adjusting section 321 was used for feedback controlto ensure that the tension at the cathode roll 325 became 160 N/m. Theclearance d corresponding to the thickness of the liquid layer at thecathode roll 1-1 at which the tension was lowest was measured by thedetecting instrument of FIG. 6, and found to be 80 μm.

The carrying speed was set at 1 m/min, and the draw ratio was setstepwise when the drive forces of the motors of the respective cathoderolls 1-1 through 1-17 were set, to gradually raise the speed and togradually raise the tension.

Control can be made in such a manner that the conductivity may bedifferent at each of the units 6 a, but in this case, the apparatusbecomes expensive. So, adjustment was made to keep the conductivity ofthe liquid layer at 2 mS/cm in all of the units 6 a, to ensure that thecopper precipitation limit should not be exceeded. That is, sulfuricacid was used as the liquid 25 for washing the doctor blade 21 in FIG.4, and its conductivity was set at 2 mS/cm. A shower was supplied for 2seconds every three minutes, to ensure that 200 ml of the liquid 25 wassupplied every two minutes. Furthermore, sulfuric acid was used as theliquid 27 supplied to the elastic body 22, and its conductivity was setat 2 mS/cm. A shower was supplied for 2 seconds every three minutes, toensure that 200 ml of the liquid 27 was supplied every 2 minutes. Inthis sequence, one minute after sulfuric acid was showered to the doctorblade 21, the liquid 27 was supplied. Moreover, sulfuric acid wassupplied as the liquid 30 supplied to the cathode roll 1, and itsconductivity was set at 2 mS/cm. A shower was supplied for 2 secondsevery three minutes, to ensure that 200 ml of the liquid 30 was suppliedevery 2 minutes. In this sequence, one minute after sulfuric acid wasshowered to the elastic body 22, the liquid 30 was supplied. In thisway, the concentration of the liquid constituting the liquid layer 8 wascontrolled.

Portions that did not satisfy the formula (i) were formed due to therelation between the clearance d corresponding to the thickness of theliquid layer and the conductivity σ, and when the film 4 a left fromeach of the cathode rolls 1, the copper precipitated on the cathode roll1 was observed. However, the precipitated copper was removed by theblade 21 and the elastic body 22, and it was confirmed that when theportion faced the film 4 a next, it was in a clean state.

Even if copper was precipitated temporarily on the surfaces of thecathode rolls 1, it was immediately removed. So, the film 4 a was notdamaged, and could be carried stably. The copper-plated film 4 b couldbe produced as a roll film having good winding style.

The blades 21 used were plastic blades E500 produced by EL Japan Co.,Ltd. The sponge of the elastic body 22 was made of PVA, and it wasuniformly pressed against the cathode roll 1, to ensure that thepressing pressure became 50 N/m.

Later, the surface of copper plating was observed, and the surface ofthe plating had few abnormal projections and depressions, and it wasconfirmed that a copper-plated film with excellent surface appearancequality could be produced. The numbers of abnormal projections anddepressions are shown in Table 3.

(3) Formation of Patterned Circuits

The film was coated with a photosensitive liquid resist and exposed toultraviolet light using a mask of a circuit pattern having 1,024 copperwires having a wire width of 30 μm at 30 μm wire intervals, i.e., at awire pitch of 60 μm, then being developed. Ferric chloride was used asan etchant for forming patterned circuits. Fifty such patterned circuitswere observed using a stereomicroscope with a magnification of 150×, andthe quality of the patterned circuits was judged in reference tochipping (a chip of 10 μm or more was identified as a defect, and apatterned circuit having even one of 1,024 wires defectively chipped wasrejected) and wire breaking. The result is shown in Table 4. Thepatterned circuits showed a yield of 100%.

Comparative Example 1

In this comparative example, a copper-plated film was applied toflexible circuit boards.

(1) Production of a Film Having a Conductive Surface

Quite the same film having a conductive surface as that of Example 1 wasproduced.

(2) Formation of a Plating Layer

The obtained 12,000 m film roll having sputtered layers was divided intofour 3,000 m rolls, to prepare four 520 mm×3,000 m film rollsrespectively having a conductive surface. One of them was passed throughthe following plating apparatus, to form a plating layer.

As the plating apparatus, the apparatus shown in FIGS. 1 and 3 was used.Copper was used as the anodes 2. Sixteen units, each of which was theunit 6 a surrounded by the one-dot-dash line of FIG. 2, were used toconstitute a plating circuit and a plating apparatus. A film 4 b havingan 8 μm thick copper plating layer was produced.

Each of the cathode rolls 1 was a SUS316 cylinder having a diameter of210 mm, a length of 800 mm and a wall thickness of 10 mm. When the film4 a was passed from the cathode roll 1-1 along the submerged roll 101-1to the cathode roll 1-2, the film pass length was 4 m. The pass lengthrefers to the length of the film 4 a from the vertex of the cathode roll1 to the vertex of the next cathode roll. Therefore, the total passlength of the plating section was 64 m.

The pretreatment conditions, plating conditions and rust preventivetreatment conditions of the film are shown in Table 1. The currentdensity for copper plating was set to ensure that the current densitygradually rose with increase in the number is of passes along thecathode roll 1 and the submerged roll 101. The currents set for therespective rectifiers 3 of the first to sixteenth units were as shown inTable 2.

The clearance d corresponding to the thickness of the liquid layer wasmeasured using the laser displacement meter 44 as shown in FIG. 6, andthe film carrying tension T was set to ensure that the clearance dbecame 300 μm or less. For setting the film tension, the tension wasadequately reduced using the S-shaped lap speed control section 309shown in FIG. 1, and then, the rotating speed of each roll was changedone after another, for drawing the film at different ratios between therespectively adjacent rolls, thereby setting the respective tensions. Atthe cathode roll (tension detection roll) 325, the pressure wasautomatically detected using a load cell, and the speed of the drivemotor of the speed adjusting section 321 was used for feedback controlto ensure that the tension at the cathode roll 325 became 160 N/m. Theclearance d corresponding to the thickness of the liquid layer at thecathode roll 1-1 at which the tension was lowest was measured by thedetecting instrument of FIG. 6, and found to be 125 μm.

The carrying speed was set at 1 m/min, and the draw ratio was setstepwise when the drive forces of the motors of the respective cathoderolls 1-1 through 1-17 were set, to gradually raise the speed and togradually raise the tension.

Ion exchange water was placed in the adjusting tank 11 of FIG. 3, andthe pump 14 was set to achieve 100 ml/min, for supplying into thereceiving pan. The conductivity of the electrolyte in the receiving pan10 in this case was 0.02 mS/cm.

As a result, the cathode rolls in the former half of carrying werelightly colored like copper on their surfaces, and the 6th to 14thcathode rolls had copper precipitated and were colored like copper ontheir surfaces. In the beginning, the carried state was stable, butafter some cathode rolls began to have copper precipitated, the carriedstate became gradually unstable, causing the film to be gripped on thecathode rolls. The film became tensioned and deflected, and beingaffected by the stirring air in the liquid, the film began to swayirregularly in the horizontal direction, and was wrinkled on the cathoderolls. Furthermore, since the copper-plated film had large stiffness,creases were also observed.

Later, the surface of copper plating was observed. The film could not beused as a product because of the creases, and even in some places freefrom creases, numerous abnormal projections of 100 μm in major axis and60 μm in height were formed here and there in the film carryingdirection. The numbers of abnormal projections and depressions are shownin Table 3.

(3) Formation of Patterned Circuits

The film was coated with a photosensitive liquid resist and exposed toultraviolet light using a mask of a circuit pattern having 1,024 copperwires having a wire width of 30 μm at 30 μm wire intervals, i.e., at awire pitch of 60 μm, then being developed. Ferric chloride was used asan etchant for forming patterned circuits. Fifty such patterned circuitswere observed using a stereomicroscope with a magnification of 150×, andthe quality of the patterned circuits was judged in reference tochipping (a chip of 10 μm or more was identified as a defect, and apatterned circuit having even one of 1,024 wires defectively chipped wasrejected) and wire breaking. The result is shown in Table 5. Thepatterned circuits showed a yield of 6%, and few normal patternedcircuits could be obtained.

Comparative Example 2

In this comparative example, a copper-plated film was applied toflexible circuit boards.

(1) Production of a Film Having a Conductive Surface

Quite the same film with a conductive surface as that of Example 1 wasproduced.

(2) Formation of a Plating Layer

The obtained 12,000 m film roll having sputtered layers was divided intofour 3,000 m rolls, to prepare four 520 mm×3,000 m film rollsrespectively with a conductive surface. One of them was passed throughthe following plating apparatus, to form a plating layer.

As the plating apparatus, the apparatus shown in FIGS. 1 and 3 was used.Copper was used as the anodes 2. Sixteen units, each of which was theunit 6 a surrounded by the one-dot-dash line of FIG. 2, were used toconstitute a plating circuit and a plating apparatus. A film 4 b havingan 8 μm thick copper plating layer was produced.

Each of the cathode rolls 1 was a SUS316 cylinder having a diameter of210 mm, a length of 800 mm and a wall thickness of 10 mm. When the film4 a was passed from the cathode roll 1-1 along the submerged roll 101-1to the cathode roll 1-2, the film pass length was 4 m. The pass lengthrefers to the length of the film 4 a from the vertex of the cathode roll1 to the vertex of the next cathode roll. Therefore, the total passlength of the plating section was 64 m.

The pretreatment conditions, plating conditions and rust preventivetreatment conditions of the film are shown in Table 1. The currentdensity for copper plating was set to ensure that the current densitygradually rose with increase in the number of passes along the cathoderoll 1 and the submerged roll 101. The currents set for the respectiverectifiers 3 of the first to sixteenth units were as shown in Table 2.

The clearance d corresponding to the thickness of the liquid layer wasmeasured using the laser displacement meter 44 as shown in FIG. 6, andthe film carrying tension T was set to ensure that the clearance dbecame 50 μm or less. For setting the film tension, the tension wasadequately reduced using the S-shaped lap speed control section 309shown in FIG. 1, and then, the rotating speed of each roll was changedone after another, for drawing the film at different ratios between therespectively adjacent rolls, thereby setting the respective tensions. Atthe cathode roll (tension detection roll) 325, the pressure wasautomatically detected using a load cell, and the speed of the drivemotor of the speed adjusting section 321 was used for feedback controlto ensure that the tension at the cathode roll 325 became 320 N/m.

The carrying speed was set at 1 m/min, and the draw ratio was setstepwise when the drive forces of the motors of the respective cathoderolls 1-1 through 1-17 were set, to gradually raise the speed and togradually raise the tension. When the film 4 a was carried, no liquidwas supplied from the adjusting tank 11 of FIG. 3.

As a result, the cathode rolls in the former half of carrying werelightly colored like copper on their surfaces, and the 6th to 14thcathode rolls had copper precipitated and were colored like copper. Inthe beginning, the film could be carried, but with the increase in thetension of the film 4 a, the film 4 a was kept tensioned for a certainperiod of time, and creased, then being fractured.

As can be seen from the above-mentioned examples and comparativeexamples, especially from the surface defects of the products shown inTable 3, the plated films produced according to the method of theinvention had very excellent appearance quality. The plated filmsproduced according to the method of the invention can be preferably usedfor producing flexible circuit boards required to have fine pitchcircuits formed.

The cathode roll for plating of the invention is described below inreference to particular examples.

To select a material resistant against the plating solution, theresistance of materials against the plating solution was examined. As aresult, it was very difficult to find a material having bothconductivity and the resistance against the plating solution.

Several milliliters of the plating solution shown in Table 1 was droppedusing a dropping pipette, and every day, the dropped plating solutionwas wiped away, to observe the resistance with eyes. A material notresistant was discolored on the surface. This work was continued for 2weeks. The results obtained after lapse of 2 weeks are shown in Table 6.Table 6 shows the examined materials and their properties. As shown inTable 6, materials mainly composed of tungsten, above all thosecontaining a predetermined amount of chromium and other elements showedexcellent plating solution resistance.

Example 3

In this example, plated films were applied to flexible circuit boards.

(1) Production of a Film Having a Conductive Surface

While a film was unwound from a film roll, it was treated in a pressurereducing device, and subsequently wound into a film roll. In thisapparatus, plasma treatment, formation of a nickel chromium layer, andformation of a copper layer were performed.

A roll of 25 μm thick, S20 mm wide and 12,500 m long polyimide film“Kapton” 1 (registered trademark of Du Pont, USA) was prearranged.

One surface of the film was treated with glow discharge plasma of argongas at a speed of 2 m/min. For the treatment, the film was carried witha distance of 2 cm kept against a rod electrode to which a high voltagewas applied, and a plasma apparatus of internal electrode system havingan electrode pair as earthed electrodes was used. The film was treatedat an argon gas pressure of 2.5 Pa, a primary output voltage of 2 kV, ahigh-frequency power supply frequency of 110 kHz and at a speed of 2m/min, to form a glow discharge plasma layer. The surface tension of thetreated film was more than 70 dynes/cm, and the contact angle was 43degrees.

Then, at an argon gas pressure of 2.6×10⁻⁶ Pa, a 30 nm nickel chromiumlayer was formed using a target consisting of 20% of chromium and 80% ofnickel by applying a DC magnetron sputtering method. Then, a 100 nmcopper layer was formed using a target consisting of copper havingpurity of 99.99 wt % by a DC magnetron sputtering method.

From the film, the testing portion for forming the sputtering layers andthe lead portion were removed to produce a 12,000 m film with sputteredlayers.

(2) Formation of a Plating Layer

The obtained 12,000 m film roll having sputtered layers was divided intofour 3,000 m rolls, to prepare four 520 mm×3,000 m film rollsrespectively with a conductive surface. Two of them were passed throughthe following plating apparatus, to form a plating layer.

As the plating apparatus, the apparatus shown in FIG. 1 was used. Copperwas used as the anodes 2. Sixteen units, each of which was the unit 6 asurrounded by the one-dot-dash line of FIG. 2, were used to constitute aplating circuit and a plating apparatus. A film 4 b having an 8 μm thickcopper plating layer was produced.

Each of the cathode rolls 1 was a SUS316 cylinder having a diameter of210 mm, a length of 1,500 mm and a wall thickness of 10 mm. The cathoderolls 1 were treated on their surfaces by the thermal spraying treatmentcorresponding to surface treatment No. 8 shown in Table 6. The thicknessof the surface treatment layer was 200 μm, and the surface roughness was0.4 μm as Rmax. The cathode rolls 1 were 0.05 mm or less in the out ofroundness, 0.08 mm or less in cylindricity, and 0.08 mm or less in therun-out in the circumferential direction. The Vickers hardness Hv of thesurfaces was 1,000.

When the film 4 a was passed from the cathode roll 1-1 along thesubmerged roll 101-1 to the cathode roll 1-2, the film pass length was 4m. The pass length refers to the length of the film 4 a from the vertexof the cathode roll 1 to the vertex of the next cathode roll. Therefore,the total pass length of the plating section was 64 m.

The pretreatment conditions, plating conditions and rust preventivetreatment conditions of the film are shown in Table 1. The currentdensity for copper plating was set to ensure that the current densitygradually rose with increase in the number of passes along the cathoderoll 1 and the submerged roll 101. The currents set for the respectiverectifiers 3 of the first to sixteenth units were as shown in Table 5.TABLE 5 Set current Rectifier No. value 3-1   20 A 3-2   32 A 3-3   50 A3-4   64 A 3-5   90 A 3-6  136 A 3-7  190 A 3-8  270 A 3-9  310 A 3-10350 A 3-11 370 A 3-12 396 A 3-13 416 A 3-14 430 A 3-15 436 A 3-16 440 ATotal 4,000 A  

TABLE 6 Surface Vickers Plating treatment Material/Surface hardness,solution No. treatment method Hv resistance 1 Hard chromium/platingtreatment 2,000 E 2 NiP-based/Plating treatment 1,700 E 3 TiN/PVDtreatment 2,000 E 4 CrN/PVD treatment 2,100 E 5 TiCr/PVD treatment 2,100E 6 W, Co, Cr, C-based/Thermal 1,000 C spraying treatment 7Cr-based/Thermal spraying treatment 950 C 8 W(70%), Cr(19%), Ni(5%),1,000 A C(6%)-based/Thermal spraying treatment 9 W(67%), Cr(20%),Ni(7%), 1,150 B C(6%)-based/Thermal spraying treatment 10  W, Co, Cr,C-based/Thermal 1,270 D spraying treatment 11  Co, Mo, Cr,Si-based/Thermal 750 D spraying treatment 12  Carburizing treatment1,100 E 13  Carbonitriding treatment 1,250 E 14  SUS316/Hardeningtreatment 300 CMeanings of the symbols in the table.A: No change after lapse of two monthsB: Slightly discolored after lapse of one monthC: Slightly discolored after lapse of one weekD: Slightly discolored after lapse of one dayE: Immediately discolored

For setting the film tension, the tension was adequately reduced usingthe S-shaped lap speed control section 309 shown in FIG. 1, and then,the rotating speed of each roll was changed one after another, fordrawing the film at different ratios between the respectively adjacentrolls, thereby setting the respective tensions. At the cathode roll(tension detection roll) 325, the pressure was automatically detectedusing each load cell, and the speed of the drive motor of the speedadjusting section 321 was used for feedback control to ensure that thetension at the cathode roll 325 became 240 N/m.

The carrying tension on each cathode roll 1 was measured using thesimple tension measuring instrument shown in FIG. 8. The tensionmeasuring instrument of FIG. 8 can measure the tension acting on a 520mm wide film.

The carrying speed was set at 1 m/min, and the draw ratio was setstepwise when the drive forces of the motors of the respective cathoderolls 1-1 through 1-17 were set, to gradually raise the speed and togradually raise the tension.

The two films 4 a were made to run in parallel to each other along therespective cathode rolls 1. The carried state of the two films was verystable.

The two 3,000 m long films 4 a were carried, and the carried positionsof 180 minutes after start of carrying are plotted as a graph shown inFIG. 9. The plan view of the plating bath section 303 of FIG. 1 in thestate where the two films 4 a-1 and 4 a-2 were carried is shown in FIG.7.

In FIG. 7, the distance in the axial direction of the cathode rolls 1 ischosen as the ordinate (Y), and the distance in the carrying directionof the films 4 a (in the direction perpendicular to the axial directionof the cathode rolls 1) is chosen as the abscissa (X).

In FIG. 7, the carrying line of the film 4 a-1 is called line A, and thecarrying line of the film 4 a-2 is called line B. Symbols A:u and A:vindicate the running positions of both the edges of the film 4 a-1, andB:u and B:v indicate the corresponding positions of the film 4 a-2. Thefilm carrying positions were very stable as shown in FIG. 9. It did nothappen that the two films 4 a-1 and 4 a-2 overlapped on each other, andthey were carried very stably.

The values of the carrying tension T measured using the measuringinstrument shown in FIG. 8 are shown in FIG. 13. From FIG. 13, it can beseen that the tension was smoothly propagated to the two films 4 a-1 and4 a-2.

Later, the surface of copper plating was observed. The surface of theplating had few abnormal projections and depressions, and it wasconfirmed that copper-plated films having excellent surface appearancequality could be produced. The numbers of abnormal projections anddepressions are shown in Table 7. No flaw was observed on the surface ofthe plating, and the surface roughness of the plating surface was 1 μmas Rmax.

(3) Formation of Patterned Circuits

The films were respectively coated with a photosensitive liquid resistand exposed to ultraviolet light using a mask of a circuit patternhaving 1,024 copper wires having a wire width of 30 μm at 30 μm wireintervals, i.e., at a wire pitch of 60 μm, then being developed. Ferricchloride was used as an etchant for forming patterned circuits. Fiftysuch patterned circuits were observed using a stereomicroscope with amagnification of 150×, and the quality of the patterned circuits wasjudged in reference to chipping (a chip of 10 μm or more was identifiedas a defect, and a patterned circuit having even one of 1,024 wiresdefectively chipped was rejected) and wire breaking. The result is shownin Table 8. The patterned circuits showed a yield of 100%. TABLE 7Number of projections and depressions in 520 mm × 100 mm Largestdiameter of Compara- Compara- projections and tive tive depressionsExample 3 Example 4 Example 3 Example 4 3 to 10 μm 10  15  >100 — 11 to50 μm 8 6 83 — 51 to 100 μm 0 0 49 — 101 μm or more 0 0 16 —

TABLE 8 Comparative Comparative Example 3 Example 4 Example 3 Example 4Number of 50 50 2 — acceptable circuits Circuits/50  100%  100%  4% —circuits

Example 4

One year later, quite the same production was performed, and as shown inFIGS. 10 and 14 and Tables 7 and 8, virtually the same results as thoseof Example 1 were obtained.

Comparative Example 3

In this comparative example, copper-plated films were applied toflexible circuit boards.

(1) Production of a Film Having a Conductive Surface

Quite the same film having a conductive surface as that of Example 1 wasproduced.

(2) Formation of a Plating Layer

The obtained 12,000 m film roll having sputtered layers was divided intofour 3,000 m rolls, to prepare four 520 mm×3,000 m film rollsrespectively with a conductive surface. Two of them were passed throughthe following plating apparatus, to form a plating layer.

As the plating apparatus, the apparatus shown in FIG. 1 was used. Copperwas used as the anodes 2. Sixteen units, each of which was the unit 6 asurrounded by the one-dot-dash line of FIG. 2, were used to constitute aplating circuit and a plating apparatus. A film 4 b having an 8 μm thickcopper plating layer was produced.

Each of the cathode rolls 1 was a SUS316 cylinder having a diameter of210 mm, a length of 1,500 mm and a wall thickness of 10 mm. The cathoderolls 1 were ground on the surfaces, to have a surface roughness of 0.6μm as Rmax after grinding. The cathode rolls 1 were 0.05 mm or less inthe roundness, 0.08 mm or less in cylindricity, and 0.08 mm or less inthe run-out in the circumferential direction. The Vickers hardness Hv ofthe surfaces was 70.

When the film 4 a was passed from the cathode roll 1-1 along thesubmerged roll 101-1 to the cathode roll 1-2, the film pass length was 4m. The pass length refers to the length of the film 4 a from the vertexof the cathode roll 1 to the vertex of the next cathode roll. Therefore,the total pass length of the plating section was 64 m.

The pretreatment conditions, plating conditions and rust preventivetreatment conditions of the film are shown in Table 1. The currentdensity for copper plating was set to ensure that the current densitygradually rose with increase in the number of passes along the cathoderoll 1 and the submerged roll 101. The currents set for the respectiverectifiers 3 of the first to sixteenth units were as shown in Table 5.

For setting the film tension, the tension was adequately reduced usingthe S-shaped lap speed control section 309 shown in FIG. 1, and then,the rotating speed of each roll was changed one after another, fordrawing the film at different ratios between the respectively adjacentrolls, thereby setting the respective tensions. At the cathode roll(tension detection roll), the pressure was automatically detected usingeach load cell, and the speed of the drive motor of the speed adjustingsection 321 was used for feedback control to ensure that the tension atthe cathode roll 325 became 240 N/m. The carrying tensions on each ofthe cathode rolls 1 were measured using load cell sensors installed onboth the sides of the cathode roll 1.

The carrying speed was set at 1 m/min, and the draw ratio was setstepwise when the drive forces of the motors of the respective cathoderolls 1-1 through 1-17 were set, to gradually raise the speed and togradually raise the tension.

The apparatus could be successfully operated for one week after start ofuse. However, thereafter, flaws gradually appeared on the surfaces ofthe cathode rolls 1, and could be visually identified. The films 4 awere gripped on the surfaces of the cathode rolls 1, and becametensioned and deflected, and being affected by the stirring air in theplating solution 7, the films 4 a began to sway irregularly in thehorizontal direction, and were wrinkled on the cathode rolls 1.Furthermore, since the copper-plated film had large stiffness, creaseswere also observed.

The two 3,000 m long films 4 a were carried, and the carried positionsof 180 minutes after start of carrying are plotted as a graph shown inFIG. 11. The plan view of the plating bath section 303 of FIG. 1 in thestate where the two films 4 a-1 and 4 a-2 were carried is shown in FIG.7. As for the running states of the two films 4 a-1 and 4 a-2, theyswayed irregularly in the horizontal direction repetitively at thepositions where the position-connecting lines are bent in FIG. 11, andthe carried states were very unstable.

The values of the carrying tension T measured using the measuringinstrument shown in FIG. 8 are shown in FIG. 15. It can be seen that thetension propagation varied at random for the two films 4 a-1 and 4 a-2.

Later, the surface of copper plating was observed. The films could notbe used as products because of the creases and even in some places freefrom creases, numerous abnormal projections of 100 μm in major axis and60 μm in height were formed here and there in the film carryingdirection. The numbers of abnormal projections and depressions are shownin Table 7. Furthermore, when the surface appearance quality wasobserved, flaws similar to the flaws of the cathode rolls 1 wereobserved, and the surface roughness was as very large as 20 μm as Rmax.It is considered that the flaws of the cathode rolls 1 were reproducedon the surfaces of the films 4 b.

(3) Formation of Patterned Circuits

The films were coated with a photosensitive liquid resist and exposed toultraviolet light using a mask of a circuit pattern having 1,024 copperwires having a wire width of 30 μm at 30 μm wire intervals, i.e., at awire pitch of 60 μm, then being developed. Ferric chloride was used asan etchant for forming patterned circuits. Fifty such patterned circuitswere observed using a stereomicroscope with a magnification of 150×, andthe quality of the patterned circuits was judged in reference tochipping (a chip of 10 μm or more was identified as a defect, and apatterned circuit having even one of 1,024 wires defectively chipped wasrejected) and wire breaking. The result is shown in Table 8. Thepatterned circuits showed a yield of 4%, and few normal patternedcircuits could be obtained.

Comparative Example 4

In this comparative example, copper-plated films were applied forflexible circuit boards.

Under quite the same conditions as in Comparative Example 1, productionoperation was repeated for 3 months. During the period, the two films 4a-1 and 4 a-2 swayed very irregularly in the horizontal direction, andoverlapped on each other. The respective films were wrinkled andcreased, and normal production could not be performed.

The 3,000 m long films 4 a-1 and 4 a-2 were carried, and the carriedpositions of 70 minutes later were plotted as a graph in FIG. 12. Theplan view of the plating bath section 303 of FIG. 1 in the state wherethe two films 4 a-1 and 4 a-2 were carried is shown in FIG. 7. As forthe running states of the two films 4 a-1 and 4 a-2, they swayedirregularly in the horizontal direction repetitively at the positionswhere the position-connecting lines are bent in FIG. 12, and the carriedstates were very unstable.

The values of the carrying tension T measured using the measuringinstrument shown in FIG. 8 are shown in FIG. 16. It can be seen that thetension propagation varied at random for the two films 4 a-1 and 4 a-2.The surfaces of the cathode rolls 1 were examined, and numerous flaws ofabout 0.5 mm in depth were observed to exist.

As can be seen from the values shown in Table 8, the copper-plated filmproduced using the cathode rolls for plating of the invention by theproduction method of the invention is very good in the surface state ofthe plating layer. Therefore, the copper-plated film is suitable forproducing flexible circuit boards formed at a fine wire pitch. Thecopper-plated film is excellent also in productivity.

INDUSTRIAL APPLICABILITY

According to the invention, a plating layer excellent in surfaceappearance quality can be formed on a conductive surface of a film, anda plated film with excellent appearance quality can be produced atexcellent productivity. The produced plated film can be preferably usedas abase of circuit boards, especially as a base of flexible circuitboards having circuits formed at a wire pitch of 60 μm or less.

1. A method for producing a plated film, in which a film carrying meansfor carrying a film having a conductive surface, a cathode roll, and aplating bath arranged in the upstream and/or downstream side of thecathode roll and accommodated with a plating solution and an anode areused, wherein the film is carried by the film carrying means, theconductive surface of the film is brought into electrical contact withthe cathode roll through a liquid layer, and passed through the platingbath for forming a plating layer on the conductive surface of the film,characterized in that the following relation is satisfied:E₀>[(I/Cs)×d]/σ where E₀ is the reduction potential of a metalconstituting the plating layer; I is the value of a current flowingthrough the cathode roll for plating; Cs is the area of the conductivesurface of the film in electrical contact with the cathode roll throughthe liquid layer; d is the thickness of a gap between the cathode rolland the conductive surface of the film; and σ is the conductivity of aliquid constituting the liquid layer.
 2. A method for producing a platedfilm, according to claim 1, wherein the conductivity of the liquidconstituting the liquid layer existing in the gap is controlled by meansof the concentration of an electrolyte mainly composed of sulfuric acid.3. A method for producing a plated film, according to claim 1, whereinthe conductivity of the liquid constituting the liquid layer existing inthe gap is from 1 mS/cm to 100 mS/cm.
 4. A method for producing a platedfilm, according to claim 1, wherein the thickness d of the gap is from20 μm to 500 μm.
 5. A method for producing a plated film, according toclaim 4, wherein the thickness d of the gap is controlled by means of acarrying tension of the film.
 6. A method for producing a plated film,according to claim 5, wherein the carrying tension of the film is from10 N/m to 320 N/m.
 7. A method for producing a plated film, according toclaim 1, wherein the plating layer is composed of copper.
 8. A methodfor producing a plated film, according to claim 1, wherein the film ismade of a polyimide resin or polyester resin.
 9. A method for producinga plated film, according to claim 1, wherein a material for constitutingthe plating layer and precipitated on a surface of the cathode roll isremoved by means of a blade and/or an elastic body provided in contactwith the surface of the cathode roll.
 10. A method for producing aplated film, according to claim 9, wherein a liquid is suppliedcontinuously or intermittently to at least one of the cathode roll, theblade and the elastic body.
 11. A cathode roll for plating used forproducing a plated film by a method, in which a film carrying means forcarrying a film having a conductive surface, a cathode roll, and aplating bath arranged in the upstream and/or downstream side of thecathode roll and accommodated with a plating solution and an anode areused in such a manner that while the film is carried by the filmcarrying means, the conductive surface of the film is brought intoelectrical contact with the cathode roll through a liquid layer, andpassed through the plating bath for forming a plating layer on theconductive surface of the film, characterized in that the surfaceroughness Rmax of the cathode roll is 1 μm or less.
 12. A cathode rollfor plating used for producing a plated film by a method, in which afilm carrying means for carrying a film having a conductive surface, acathode roll, and a plating bath arranged in the upstream and/ordownstream side of the cathode roll and accommodated with a platingsolution and an anode are used in such a manner that while the film iscarried by the film carrying means, the conductive surface of the filmis brought into electrical contact with the cathode roll through aliquid layer, and passed through the plating bath for forming a platinglayer on the conductive surface of the film, characterized in that theVickers hardness of the surface of the cathode roll is 200 or more. 13.A cathode roll for plating, according to claim 11 or 12, which has asurface layer mainly composed of tungsten.
 14. A cathode roll forplating, according to claim 11 or 12, which has a surface layercontaining 50 wt % or more of tungsten and further containing at leastone element selected from the group consisting of chromium, nickel andcarbon.
 15. A cathode roll for plating, according to claim 11 or 12,which has a surface layer containing 60 to 80 wt % of tungsten, 15 to 25wt % of chromium, 1 to 10 wt % of nickel, and 1 to 10 wt % of carbon.16. A cathode roll for plating, according to claim 11 or 12, which istreated on the surface by a thermal spraying method.
 17. A cathode rollfor plating, according to claim 16, wherein the thermal spraying methodis a detonation flame spraying method.
 18. A cathode roll for plating,according to claim 16, wherein the porosity of a thermally sprayed layerformed by surface treatment based on the thermal spraying method is 2%or less.
 19. A method for producing a plated film, in which a filmcarrying means for carrying a film having a conductive surface, acathode roll, and a plating bath arranged in the upstream and/ordownstream side of the cathode roll and accommodated with a platingsolution and an anode are used, wherein the film is carried by the filmcarrying means, the conductive surface of the film is brought intoelectrical contact with the cathode roll through a liquid layer, andpassed through the plating bath for forming a plating layer on theconductive surface of the film, characterized in that the cathode rollis a cathode roll for plating as set forth in claim 11 or
 12. 20. Amethod for producing a circuit board by forming a circuit pattern on aplated film, characterized in that the plated film is a plated filmproduced by the method for producing a plated film as set forth in anyone of claims 1 to 12.